I'm pretty sure CASE (Crankshaft Angle Sensor Error) relearn is for PCM crankshaft variation. I don't think this has anything to do with the security system, BCM or ignition switch replacement.
I did some more research and found that you most likely have a PK3 security system. Please read the following:
PASSKEY 3 AND PASSKEY 3+
In this system, the vehicle theft deterrent functions are provided by the theft deterrent control module. There is a transponder embedded in the head of the key that becomes energized by the exciter coils in the ignition lock cylinder when the ignition switch is turned on. The energized transponder now transmits a signal containing a unique value to the theft deterrent control module. If the module accepts this value, then there is an additional communication that takes place between the module and the key. If the module and the key agree, then the module sends the fuel enable password to the PCM. If the PCM recognizes the password, then the vehicle starts and runs normally. If any of the communication between the module and the key is incorrect or the PCM does not recognize the password, then the fuel injectors are disabled. The ignition key is a normal looking key with no visible contacts as in the Passkey or VATS systems. The transponder is located in the key head. The transponder value is fixed and cannot be changed. These keys are usually identified by the letters PK3, or PK3+ stamped into the steel body. A relearn will be necessary if any of the following have been replaced: any key, the theft deterrent control module or the powertrain control module (PCM). When the theft control module is being replaced, the module will learn the existing keys immediately. However, the PCM must learn the new fuel enable password from the new module. If you are replacing a PCM with a PCM that has been used in another vehicle or has been remanufactured, then a relearn must be performed in order for the PCM to learn the fuel enable password. Keep in mind that when you perform a relearn on this system, all previously learned keys will be erased from the theft deterrent control module’s memory. Any additional keys may be relearned immediately after the first relearn has been performed by inserting the additional key and turning the ignition switch to the “On” position within ten seconds of removing the previously learned key.
In order to initiate the relearn process:
1. Insert a master key (black head) into the ignition switch.
2. Turn to the “On” position without starting the engine. The security light should illuminate and stay on.
3. Wait approximately 10 minutes or until the security light turns off.
4. Turn off the ignition switch and wait 5 seconds.
5. Repeat steps 2 through 4 two more times with the same key.
6. Turn the ignition off. The vehicle will now learn the key transponder information on the next start cycle.
7. Start the vehicle. If vehicle starts and runs normally, and security light is off, the relearn is complete.
